NAME

       outb,  outw,  outl,  outsb, outsw, outsl, inb, inw, inl, insb, insw, insl, outb_p, outw_p, outl_p, inb_p,
       inw_p, inl_p - port I/O

SYNOPSIS

       #include <sys/io.h>

       unsigned char inb(unsigned short int port);
       unsigned char inb_p(unsigned short int port);
       unsigned short int inw(unsigned short int port);
       unsigned short int inw_p(unsigned short int port);
       unsigned int inl(unsigned short int port);
       unsigned int inl_p(unsigned short int port);

       void outb(unsigned char value, unsigned short int port);
       void outb_p(unsigned char value, unsigned short int port);
       void outw(unsigned short int value, unsigned short int port);
       void outw_p(unsigned short int value, unsigned short int port);
       void outl(unsigned int value, unsigned short int port);
       void outl_p(unsigned int value, unsigned short int port);

       void insb(unsigned short int port, void *addr,
                  unsigned long int count);
       void insw(unsigned short int port, void *addr,
                  unsigned long int count);
       void insl(unsigned short int port, void *addr,
                  unsigned long int count);
       void outsb(unsigned short int port, const void *addr,
                  unsigned long int count);
       void outsw(unsigned short int port, const void *addr,
                  unsigned long int count);
       void outsl(unsigned short int port, const void *addr,
                  unsigned long int count);

DESCRIPTION

       This family of functions is used to do low-level port input and  output.   The  out*  functions  do  port
       output, the in* functions do port input; the b-suffix functions are byte-width and the w-suffix functions
       word-width; the _p-suffix functions pause until the I/O completes.

       They are primarily designed for internal kernel use, but can be used from user space.

       You must compile with -O or -O2 or similar.  The functions are defined as inline macros, and will not  be
       substituted in without optimization enabled, causing unresolved references at link time.

       You  use  ioperm(2)  or  alternatively  iopl(2) to tell the kernel to allow the user space application to
       access the I/O ports in  question.   Failure  to  do  this  will  cause  the  application  to  receive  a
       segmentation fault.

CONFORMING TO

       outb()  and  friends  are hardware-specific.  The value argument is passed first and the port argument is
       passed second, which is the opposite order from most DOS implementations.

SEE ALSO

       ioperm(2), iopl(2)

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.